I would agree that the portrait was probably done by one of Henri’s students. The likeliness is so good that either the painter had the access to the model or he had to make a copy out of an original one. But the differernt poses in two paintings suggest that latter is unlikely. Willie was not a professional model, and probably only some of Henri’s students could have access and interest to paint someone who would not be able to afford a portraiture.
Starting from 1902, Robert Henri began to teach at New York School of Art. A bunch of artists went to his studio. Considering that so many of his pupils became well-known, it is worth investigating to know the possible painter of this Wilie Gee portrait. To my surprise, the painting did not sell (based on the preliminary sale results). Maybe the quest for the identifying the real painter of this Willie Gee may keep going.